1. Field of the Invention
The present invention relates to an elastic wave device, a high-frequency front end circuit including the elastic wave device, and a communication apparatus.
2. Description of the Related Art
Elastic wave devices have been widely used for band pass filters for cellular phones. For example, in an elastic wave device described in Japanese Unexamined Patent Application Publication No. 2014-187568, a dielectric film is provided on a piezoelectric substrate such that the dielectric film covers an interdigital transducer (IDT) electrode. The elastic wave device utilizes Rayleigh waves. The piezoelectric substrate is a lithium niobate (LiNbO3) substrate. The dielectric film is made of SiO2. The interdigital transducer electrode contains molybdenum (Mo). Accordingly, the frequency-temperature characteristics are improved.
However, an inventor of the present application has first discovered a problem that in an elastic wave device utilizing Rayleigh waves and including a piezoelectric substrate made of lithium niobate, an interdigital transducer electrode containing molybdenum, and a dielectric film which covers the interdigital transducer electrode, the frequency-temperature characteristics degrade depending on the duty ratio of the dielectric film and, thus, manufacturing variations occur in the line width of an electrode finger of the interdigital transducer electrode.
If variations occur in the frequency of the elastic wave device, in a case in which a different frequency band is present near a pass band of the elastic wave device, for example, in the case of a transmission band Tx and a reception band Rx of Band 8, the variations may adversely affect the different frequency band. Therefore, desired filter characteristics may not be achieved.